The present invention generally relates to a universal parallel ruler for use with a three-dimensional drawing such as an isometric projection, a dimetric projection or anisometric projection. Basically, the three-dimensional drawing is defined by three planes and all the circles contained in these three planes, corresponding to holes, shafts, etc., are drawn in ellipses. Each ellipse is determined by the ratio of its major and minor axes and the practical operation of drafting is performed using a template including many ellipses of various ratios arranged therein. In the universal parallel ruler for three-dimensional drawing of prior art, in which three scales correspond to the basic three axes, one of the serious problems relates to the fact that the three scales interfere with one another for effective use of the template. Each of the ellipses drawn in the basic three planes is determined by major and minor axes which are always perpendicular to each other. In view of these aspects, a universal parallel ruler having two scales always held perpendicular to each other will be extremely advantageous for use with a three-dimensional drawing in that the template can be used without any interference with the scales and that the respective basic three axes and lines transverse to each of these basic three axes can be immediately obtained.
The means to set the scales at an interval of 15.degree. or 30.degree. by cooperation of the index plate is mounted on the head support and a locking pawl is provided on the movable part of the head (i.e., on the scale side) of a universal parallel ruler. But this type of ruler has two scales at intermediate angles which correspond neither to 15.degree. nor to 30.degree.. The same problem remains even when the index plate is movably arranged and adapted to be fixed at an optional position relative to its associated support, since only one of the basic three axes could be position-set. The other two axes have positions which vary for every three-dimensional drawing.
In accordance with the present invention, the problem as described just above is overcome by an arrangement such that the head is provided with preset stoppers principally adapted to be optionally position-adjusted according to the basic three axes of a three-dimensional drawing and the scales can be selectively set to the basic three axes which vary angularly for each three-dimensional drawing. The preset stopper corresponding to the vertical axis of the basic three axes of the three-dimensional drawing may be stationarily provided since the vertical axis is, in most cases, drawn as a vertical line. Furthermore, according to the present invention, there is provided an arrangement such that a single locking piece is engaged with or disengaged from the preset stoppers respectively corresponding to the basic three axes so that the scales may be selectively engaged with or disengaged from the respective preset stoppers which have already been angularly set. In further preferred embodiment, the angularly adjustable preset stoppers can be fixably mounted by associated clamp members on the protractor. Therefore, the basic three axes can be independently set. The present invention also enables the scales to be set by operatively associating the protractor with the scales relative to a stationary index and fixing the protractor at a desired position relative to the three axes.
Accordingly, one object of the present invention is to provide a universal parallel ruler for three-dimensional drawings which overcomes all of the previously described disadvantages present in parallel rulers of the prior art.
Another object of present invention is to provide a universal parallel ruler having a head which is further provided with preset stoppers which are adapted to be position adjustable according to the angular position of the basic three axes in the three-dimensional drawing.
A further object of the present invention relates to the provision of a single locking piece which operates a mechanism which is further engagable and disengagable with all of the aforementioned preset stoppers so that one of the scales of the parallel ruler can be set to a position corresponding to the position occupied by one of the three axes in the three-dimensional drawing.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.